Microbial tradeoffs in internal and external use of resources regulated by phosphorus and carbon availability

A general strategy in modern agriculture to reduce phosphorus (P) fertilization is to rely on microbial efficiency of P acquisition and recycling from organic sources. However, this involves extracellular enzymes that require energy from ATP, so the process depends on the microbes' physiological state and soil P availability. To elucidate the key relationships we compared P acquisition processes in P-poor soil (Cambisol) and links between C:P stoichiometry, enzyme activity, and ATP with microbial communities in contrasting activity states (dormancy, growth followed by starvation and gradually activated, respectively induced by no, single large (50 mu g C g(-1) soil) and multiple low (five days of 10 mu g C g(-1) soil day(-1)) additions of glucose as a carbon (C) source). A sole P input, without C addition, almost doubled microbial C (C-mic) contents, maintained stable phosphatase activity at 36 nmol h(-1) per nmol ATP and raised microbial P (P-mic) 2.7-fold. In contrast, sole glucose addition increased P-mic by only 8%, confirming that P-limitation was much stronger than C limitation. Only 5-10 % of P potentially mineralized by phosphatase was recovered as microbial P. C-mic:P-mic ratios in microbial biomass 200 and 350 respectively reflected C starvation and strong P starvation. The ATP was a suitable predictor of microbial biomass in soil lacking fresh substrate, but weak predictor of microbial biomass after substrate input. Structural equation models revealed contrasting strategies of P utilization depending on microbial activity state. Dormant microorganisms (without glucose addition) invested most P to ATP production. In contrast, following substrate addition P-limited microorganisms accelerated phosphatase production, and hence capacity to mine P in organic sources. Thus, the P utilization/acquisition strategies depended on C accessibility and were modulated by P availability.

Automated summary

A common strategy in modern agriculture to reduce phosphorus fertilization is relying on microbial efficiency in acquiring and recycling phosphorus from organic sources. The study found that phosphorus limitation was stronger than carbon limitation, and microbial utilization of phosphorus depended on microbial activity state. Different microbial activity states showed contrasting phosphorus utilization strategies, with dormant microorganisms investing most phosphorus in ATP production, while phosphorus-limited microorganisms accelerated phosphatase production to mine phosphorus in organic sources.